1. Field of the Invention
The invention relates to electroacoustic microphone transducer, functioning according to the electrostatic principle, comprising a high-resistance pre-amplifier arranged in the microphone capsule on a printed board and a post-amplifier arranged also on a printed board.
2. Description of the Related Art
Electroacoustic microphone transducers functioning according to the electrostatic principle have two metal surfaces forming the electrodes of an electric capacitor. The movable electrode is a diaphragm that is mounted with its edge so as to vibrate freely and is usually simply referred to as diaphragm. The stationary electrode is simply referred to as electrode and is manufactured of an electrically conducting material and provided with several openings. It is immobile and, because of its perforations, allows sound to pass through. The changes of the sound pressure acting on the diaphragm of the microphone transducer cause the movement of the diaphragm and thus the changes of the electrical capacitance of the microphone transducer.
In order to be able to transform the changes of the electrical capsule capacitance into the voltage changes at the output terminals of the microphone, it is necessary to generate an electrical field between the electrodes of the microphone capsule. This can be done in two ways. Either a so-called polarization voltage is generated between the electrodes of the microphone capsule by means of a voltage source (this is referred to as capacitor transmitter) or, by means of a material that has excellent electrical insulating properties (for example, Teflon®), one of the electrodes is provided permanently with charges and the applied layer is used as an electrical charge carrier and storage device (this is a so-called electret transducer).
Both configurations have in common that the transducer system, when viewed electrically, has high resistance. This means that the amplifier arranged downstream must firstly also be configured with a high-resistance input impedance and, secondly, for the purpose of electromagnetic shielding, the amplifier must be mounted in direct vicinity of the microphone capsule. The last condition is adhered to so strictly that the first stage of the microphone amplifier, as a so-called impedance transducer, is arranged in the housing of the microphone capsule itself. Such a configuration according to the prior art is illustrated in FIG. 1 and will be discussed in the following.
An electrostatic microphone capsule configured in this way has at least two electrical contacts or terminals. With these contacts, the microphone capsule is connected to the amplifier. Contacting can be realized by solder contacts or terminal contacts. Both types of contacting have in common that they increase the costs of the microphone capsule and, primarily, they represent a source of malfunctions.